EXPLANATION OF PLATE 18 



Fig. 1. Mytilus (Mytilocuncha) mathewsonii Gabb. Type, taken from Gabb 's 

 figure in Geol. Surv. Calif., Palaeontology, vol. 2, see. 1, p. 30, pi. 8, fig. 51, 1860. 

 Natural size. 



Fig. 2. Mytilus (MytUoconoha) mathewsonii Gabb. View of binge, showing 

 characteristic groove under the beak of subgenus Mytiloeoncha. No. 11282, Coll. 

 Invert. Palae. Univ. Calif., loe. 1131. Natural size. 



